The present invention relates to novel monomers used for preparing a photoresist copolymer, copolymers thereof, and photoresist compositions prepared therefrom. More specifically, it relates to such novel monomers, copolymers and photoresist compositions suitable to be exposed to light in the far ultraviolet region of the spectrum.
A photosensitive film for use with far ultraviolet light, in particular, for ArF radiation, must satisfy several requisites; it must have low light absorbance at a wavelength of 193 nm, excellent etching resistance and adhesiveness to a substrate, and be developable in an aqueous solution of 2.38% or 2.6% tetramethylammonium hydroxide (hereinafter, abbreviated as TMAH). Up to the present time, researchers have focused on searching for a substance having as high transparency and etching resistance at 193 mn as novolac resins. For example, researchers at the Bell Labs Research Center have enhanced etching resistance of photoresist copolymers by adding an alicyclic unit to the main chain. In addition, researchers at Fujitsu of Japan and Sipri of the United States are actively investigating methacrylate and acrylate compounds as photoresist polymers. However, these techniques have not solved the problem of etching resistance, and involve increased production costs resulting from the introduction of alicyclic groups into the polymer. In addition, the low adhesiveness exhibited by most prior art photoresists is disadvantageous in that photolithographic patterns cannot be established with integrated L/S patterns of 150 nm or less.
An object of the present invention is to solve the problems described above, and to provide novel monomers which can be used to form copolymers which have excellent adhesiveness and sensitivity, and which can be easily produced at low production cost, and to provide a process for preparing the monomers.
Another object of the present invention is to provide copolymers of the novel monomers, and a process for preparing the same.
Another object of the present invention is to provide photoresist compositions using the copolymers and a process for preparing the same.
Still another object of the present invention is to provide a semiconductor element produced by using the photoresist composition.
The present invention provides a novel compound represented by following Chemical Formula 1:.
wherein,
R is substituted or non-substituted linear or branched (C1-C10) alkyl, substituted or non-substituted (C1-C10) ether, substituted or non-substituted (C1-C10) ester, or substituted or non-substituted (C1-C10) ketone;
X and Y are independently CH2, CH2CH2, oxygen or sulfur; and
i is 0 or an integer of 1 to 2.
In order to achieve other technical objects, photoresist copolymer comprising repeating units of the monomer of Formula 1 are provided by another embodiment of the present invention. Preferred copolymers are represented by following Chemical Formulas 100 and 100a:. 
wherein,
R is substituted or non-substituted linear or branched (C1-C10) alkyl, substituted or non-substituted (C1-C10) ether, substituted or non-substituted (C1-C10) ester, or substituted or non-substituted (C1-C10) ketone;
X, Y, V and W are independently CH2, CH2CH2, oxygen or sulfur;
i and j are independently 0 or an integer of 1 to 2;
R* is an acid-reactable group; and
a, b and c represent the polymerization ratio of the monomers.
In the case of the chemical formula 100, it is preferred that a:b:cxe2x80x94(0.01-0.2):(0.1-0.4): 0.5 in molar equivalent ratio.
The photoresist composition according to the present invention comprises (i) a photoresist copolymer according to the present invention, a photoacid generator and a conventional organic solvent.
Hereinafter, the present invention will be described in detail.
Compounds of Chemical Formula 1 have been found to be particularly useful for preparing chemically amplified photoresist copolymers. Compounds of Chemical Formula 1 have a HYDROXY group which can enhance adhesiveness of the photoresist to a wafer substrate and a carboxylic acid group which can contribute to the enhancement of photo-sensitivity at the same time. In addition, the compounds can be simply synthesized without toxic odors and are readily crystallized in water without using any complicated separating means such as distillation or column chromatography. Thus, compounds of the present invention are advantageous in mass production at low cost.
In preferred compounds of Chemical Formula 1, R is represented by the following Chemical Formula 1a:
xe2x80x94(CH2)mxe2x80x94Zxe2x80x94(CH2)nxe2x80x94
wherein
Z is a moiety of the formula xe2x80x94C(R1)(R2)xe2x80x94 or oxygen;
R1 and R2 are independently H or an (C1-C5) alkyl; and
m and n are independently 0 or an integer of 1 to 5.
The photoresist monomer according to the present invention can be prepared by reacting (i) a di-alcohol such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol and diethylene glycol and (ii) an anhydride such as 5-norbornene-2,3-dicarboxylic anhydride and exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride, in an organic solvent such as tetrahydrofuran, dimethylformamide, dioxane, benzene and toluene.
For example, the compound represented by the following Chemical Formula 2, one of the compounds represented by the above Formula 1, can be obtained by reacting a compound of Chemical Formulas 2a and 2b in the presence of an acid catalyst or a base: 
wherein, Y is CH2, CH2CH2, oxygen or sulfur;
Z is a moiety of the formula xe2x80x94C(R1)(R2)xe2x80x94 or oxygen;
R1 and R2 are independently H or an (C1-C5) alkyl; and
m and n are independently 0 or an integer of 1 to 5.
The compound of Chemical Formula 2a may be used in the same amount or in an excess amount relative to the compound of Chemical Formula 2b.
NaH, KH, CaH2, Na2CO3, LDA (lithium diisopropylamide) or the like may be used as a base, and sulfuric acid, acetic acid or nitric acid may be used as an acid catalyst.
Novel monomers according to the present invention (the compounds represented by Chemical Formula 1) can also be prepared by a Diels-Alder reaction. For example, the compound represented by the above chemical formula 2 can be prepared by following Reaction Schemes (1) and (2) below: 
wherein
Y is CH2, CH2CH2,, oxygen or sulfur;
Z is a moiety of the formula xe2x80x94C(R1)(R2)xe2x80x94 or oxygen;
R1 and R2 are independently H or an (C1-C5) alkyl; and
m and n are independently 0 or an integer of 1 to 5.
That is, first, the intermediate material is obtained by reacting maleic anhydride and di-alcohol in an organic solvent such as benzene, tetrahydrofuran, dimethylformamide or dioxane in the presence of an acid catalyst, as shown in the Reaction Scheme 1, and then, the final product material is obtained by a Diels-Alder reaction which is performed in an organic solvent such as benzene and tetrahydrofuran, as shown in the Reaction Scheme 2.
Preferred photoresist copolymers according to the present invention comprise repeating units of a compound of Chemical Formula 1 as a first comonomer and a compound of the following Chemical Formula 3 as the second comonomer: 
wherein,
V and W are independently CH2, CH2CH2, oxygen or sulfur;
j is 0 or an integer of 1 to 2; and
R* is an acid reactable group.
In the Chemical Formula 3, the R* is released when it is reacted with the acid produced by the photoacid generator in the photoresist composition. Thus, while the photoresist polymer in exposed regions of the photoresist layer becomes soluble in the developing solution, the polymer in the unexposed regions is not dissolved in the developing solution because acid is not generated therein and therefore the acid-reactable groups are still bound to the photoresist polymer. As the result, a predetermined pattern is formed.
Accordingly, the compounds of Chemical Formula 3 have a role in enhancing the photosensitivity of the photoresist polymer by increasing the difference in solubility in the developing solution between the exposed portion and the unexposed portion.
Suitable acid-reactable (acid labile) groups include tert-butyl, 2-tetrahydrofuranyl, 2-tetrahydropyranyl, 2-ethoxyethyl, t-butoxyethyl and so on. In a most preferred embodiment, the second comonomer is tert-butyl-5-norbornene-2-carboxylate, the compound of following Chemical Formula 3a: 
Maleic anhydride or maleimide derivatives can be added as polymerization-enhancing monomers for making the polymerization between the cycloolefin compounds more efficient. However, when performing polymerization using a metal catalyst, such a polymerization-enhancing monomer is not necessarily required.
The first comonomer of Formula 1 and the second comonomer of Formula 3 comprising the photoresist copolymer according to the present invention each contain substituents having large steric hindrance. Therefore, in preferred copolymers a spacer comonomer, such as the compound of the following Chemical Formula 4, is added to the main polymer chain in order not only to reduce the steric hindrance (thus increasing the synthetic yield, preferably to over 40%), but also to properly adjust the molecular weight to a desirable range (preferably, in the range of 7,000-8,000). 
wherein,
U is CH2, CH2CH2, oxygen or sulfur; and
Rxe2x80x2 is hydrogen or C1-C5 alkyl.
More preferred, the Rxe2x80x2 is hydrogen or methyl.
The following Chemical Formulas 100, 200, 100a and 200a represent preferred photoresist copolymers according to the present invention. 
wherein,
X, Y, V, W and U are independently CH2, CH2CH2, oxygen or sulfur;
R is substituted or non-substituted linear or branched (C1-C10) alkyl, substituted or non-substituted (C1-C10) ether, substituted or non-substituted (C1-C10) ester, or substituted or non-substituted (C1-C10) ketone;
R* is an acid-reactable group;
Rxe2x80x2 is hydrogen or C1-C5 alkyl;
i and j are independently 0 or an integer of 1 to 2; and
a, b, c and d are independently the polymerization ratio of the comonomers.
The molecular weight of the photoresist copolymers according the to present invention is 3,000 to 12,000, preferably, 5,000 to 10,000.
While the copolymers represented by the Chemical Formulas 100 and 200 are mainly obtained by a synthesizing method using a polymerization initiator, the copolymers represented by the Chemical Formulas 100a and 200a are mainly obtained by a synthesizing method using a metal catalyst.
A synthesizing method using a polymerization initiator is performed by reacting the comonomers in an organic solvent in the presence of a polymerization initiator. Presently preferred organic solvents include tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, dioxane, methyl ethyl ketone, benzene, toluene or xylene may be used. Conventional radical polymerization initiators, such as 2,2-azobisisobutyronitile (AIBN), acetyl peroxide, lauryl peroxide and tert-butyl peroxide may be used in the synthesis of the copolymers of the present invention.
Photoresist compositions according to the present invention, which are useful for photolithography processes employing a deep ultraviolet light source such as ArF, may be prepared by dissolving a photoresist copolymer according to the present invention together with a conventional photoacid generator in a conventional organic solvent.
Sulfide or onium type compounds are preferably used as the photoacid generator. The photoacid generator may be one or more compounds selected from the group consisting of diphenyl iodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate, diphenyliodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate, diphenyl p-toluenyl triflate, diphenyl p-isobutylphenyl triflate, diphenyl p-tert-butylphenyl triflate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroarsenate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium triflate and dibutylnaphthylsulfonium triflate. The photoacid generator is used in an amount of 0.05 to 10% by weight of the photoresist copolymer employed. If the amount of the photoacid generator is less than 0.05% by weight, photosensitivity of the photoresist becomes poor. On the other hand, if the amount is more than 10%, the photoacid generator readily absorbs deep ultraviolet to provide a pattern having poor cross-sectional surface.
A conventional organic solvent, such as ethyl 3-ethoxypriopionate, methyl 3-methoxypropionate, cyclohexanone, propylene glycol methyl ether acetate, or the like, may be used in the photoresist compositions of the present invention. The amount of solvent used is 200 to 1000% by weight of the photoresist copolymer, in order to obtain a photoresist layer of desirable thickness. According to the experiments by the present inventors, when the amount of solvent is 600% by weight, a photoresist layer having a thickness of 0.5 xcexcm is obtained.
A conventional photoresist pattern-forming method can be used with the photoresist composition prepared according to the present invention, for example as follows:
First, the photoresist composition of the present invention is spin-coated on a silicon wafer to form a thin film, which is then soft-baked (i.e. heated in an oven or on a hot plate at 70 to 200xc2x0 C., preferably at 80 to 150xc2x0 C. for 1 to 5 minutes), and exposed to light by using an exposing device employing a deep ultraviolet light source, such as ArF light and KrF light, which has a wavelength below 250 nm. Then, the wafer is post-baked (i.e. heated at 70 to 200xc2x0 C., more preferably, 100 to 200xc2x0 C.). Then, the wafer is impregnated in 2.38% aqueous TMAH developing solution for 1.5 minutes, to obtain a photoresist image.
In the above procedure, the exposure energy is preferably 0.1 to 30 mJ/cm2 and, instead of the deep ultraviolet light source, an E-beam, X-ray, EUV, VUV(Vacuum Ultra Violet) or similar light source may be used.
By employing the photoresist composition according to the present invention, a line/space (L/S) photoresist pattern having excellent adhesiveness and resolution is obtained, without patten collapse, even when isolation is not more than 70 nm.
According to the present invention, a photoresist composition having excellent etching resistance and adhesiveness can be manufactured in large scale with low production cost, and a semiconductor element having excellent reliability can be prepared therefrom.